Cleaning Compound and Method and System for Using the Cleaning Compound

ABSTRACT

A cleaning compound is provided. The cleaning compound includes about 0.1 weight percent to about 10 weight percent of a fatty acid dispersed in water. The cleaning compound includes an amount of a base sufficient to bring a pH of the fatty acid water solution to about a level where above about 50% of the dispersed fatty acid is ionized. A method for cleaning a substrate, a system for cleaning a substrate, and a cleaning solution prepared by a process are also provided.

CLAIM OF PRIORITY

This application is a divisional application of U.S. patent applicationSer. No. 12/705,445, filed on Feb. 12, 2010, entitled “Cleaning Compoundand Method and System for Using the Cleaning Compound,” which is adivisional application of U.S. patent application Ser. No. 11/347,154,filed on Feb. 3, 2006, entitled “Cleaning Compound and Method and Systemfor Using the Cleaning Compound,” which 1) claims the benefit of U.S.Provisional Patent Application No. 60/755,377, filed on Dec. 30, 2005,and 2) is a continuation-in-part application of U.S. application Ser.No. 10/608,871, filed on Jun. 27, 2003, entitled “Method and Apparatusfor Removing a Target Layer From a Substrate Using Reactive Gases.” Thedisclosure of each of the above-identified applications is incorporatedherein by reference in its entirety for all purposes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No.10/816,337, filed on Mar. 31, 2004, and entitled “Apparatuses andMethods for Cleaning a Substrate,” and U.S. patent application Ser. No.11/173,132, filed on Jun. 30, 2005, and entitled “System and Method forProducing Bubble Free Liquids for Nanometer Scale SemiconductorProcessing,” and U.S. patent application Ser. No. 11/153,957, filed onJun. 15, 2005, and entitled “Method and Apparatus for Cleaning aSubstrate Using Non-Newtonian Fluids,” and U.S. patent application Ser.No. 11/154,129, filed on Jun. 15, 2005, and entitled “Method andApparatus for Transporting a Substrate Using Non-Newtonian Fluid,” andU.S. patent application Ser. No. 11/174,080, filed on Jun. 30, 2005, andentitled “Method for Removing Material from Semiconductor Wafer andApparatus for Performing the Same,” and U.S. patent application Ser. No.10/746,114, filed on Dec. 23, 2003, and entitled “Method and Apparatusfor Cleaning Semiconductor Wafers using Compressed and/or PressurizedFoams, Bubbles, and/or Liquids,” and U.S. Pat. No. 7,648,584, issuedJan. 19, 2010, entitled “Method and Apparatus for Removing Contaminationfrom Substrate.” The disclosure of each of these related applications isincorporated herein by reference for all purposes.

BACKGROUND

In the fabrication of semiconductor devices such as integrated circuits,memory cells, and the like, a series of manufacturing operations areperformed to define features on semiconductor wafers (“wafers”). Thewafers include integrated circuit devices in the form of multi-levelstructures defined on a silicon substrate. At a substrate level,transistor devices with diffusion regions are formed. In subsequentlevels, interconnect metallization lines are patterned and electricallyconnected to the transistor devices to define a desired integratedcircuit device. Also, patterned conductive layers are insulated fromother conductive layers by dielectric materials.

During the series of manufacturing operations, the wafer surface isexposed to various types of contaminants. Essentially any materialpresent in a manufacturing operation is a potential source ofcontamination. For example, sources of contamination may include processgases, chemicals, deposition materials, and liquids, among others. Thevarious contaminants may deposit on the wafer surface in particulateform. If the particulate contamination is not removed, the deviceswithin the vicinity of the contamination will likely be inoperable.Thus, it is necessary to clean contamination from the wafer surface in asubstantially complete manner without damaging the features defined onthe wafer. The size of particulate contamination is often on the orderof the critical dimension size of features fabricated on the wafer.Removal of such small particulate contamination without adverselyaffecting the features on the wafer can be quite difficult.

Conventional wafer cleaning methods have relied heavily on mechanicalforce to remove particulate contamination from the wafer surface. Asfeature sizes continue to decrease and become more fragile, theprobability of feature damage due to application of mechanical force tothe wafer surface increases. For example, features having high aspectratios are vulnerable to toppling or breaking when impacted by asufficient mechanical force. To further complicate the cleaning problem,the move toward reduced feature sizes also causes a reduction in thesize of particulate contamination that may cause damage. Particulatecontamination of sufficiently small size can find its way into difficultto reach areas on the wafer surface, such as in a trench surrounded byhigh aspect ratio features or bridging of conductive lines, etc. Thus,efficient and non-damaging removal of contaminants during modernsemiconductor fabrication represents a continuing challenge to be met bycontinuing advances in wafer cleaning technology. It should beappreciated that the manufacturing operations for flat panel displayssuffer from the same shortcomings of the integrated circuitmanufacturing discussed above. Thus, any technology requiringcontaminant removal is in need of a more effective and less abrasivecleaning technique.

SUMMARY

Broadly speaking, the present invention fills these needs by providingan improved cleaning technique and cleaning solution. It should beappreciated that the present invention can be implemented in numerousways, including as a system, an apparatus and a method. Severalinventive embodiments of the present invention are described below.

In one embodiment, a cleaning compound is provided. The cleaningcompound includes about 0.5 weight percent to about 10 weight percent ofa fatty acid dissolved in water. The cleaning compound includes anamount of a base sufficient to bring a pH of the fatty acid watersolution to about a level above where about 50% of the dissolved fattyacid is ionized.

In another embodiment, a method of cleaning a substrate is provided. Themethod includes applying an emulsion having a first immiscible liquidcombined with a second immiscible liquid to a surface of the substrate.The second immiscible liquid forms a plurality of droplets dispersedwithin the first immiscible liquid, and the emulsion further includessolid particles distributed within the first immiscible liquid. A forcehaving a normal component is applied to one of the solid particles tobring the one of the solid particles within an interaction range of acontaminant on the surface of the substrate. The one of the solidparticle and the contaminant are removed from the surface of thesubstrate.

In yet another embodiment, a system for cleaning a substrate isprovided. The system includes a cleaning head configured to be disposedover a surface of the substrate, the cleaning head having multiplecleaning portions. The system includes a cleaning solution reservoirsupplying a cleaning solution to one of the multiple cleaning portions.The cleaning solution has a dispersed phase, a continuous phase andparticles dispersed within the continuous phase.

In still yet another embodiment, a process for preparing a solution forcleaning a substrate is provided. The process includes preparing asolution of a fatty acid in a solvent within a specified concentrationrange and adding water to the fatty acid solution. The process alsoincludes stabilization of the solution by adding a surface-activesubstance or by ionizing the fatty acid in the solution.

Other aspects and advantages of the invention will become more apparentfrom the following detailed description, taken in conjunction with theaccompanying drawings, illustrating by way of example the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be readily understood by the followingdetailed description in conjunction with the accompanying drawings, andlike reference numerals designate like structural elements.

FIG. 1 is an illustration showing a physical diagram of a cleaningmaterial for removing contamination from a semiconductor wafer, inaccordance with one embodiment of the present invention.

FIGS. 2A-2B are illustrations showing how the cleaning materialfunctions to remove the contaminant from the wafer, in accordance withone embodiment of the present invention.

FIG. 3 is an illustration showing a flowchart of a method for removingcontamination from a substrate, in accordance with one embodiment of thepresent invention.

FIG. 4 is a simplified schematic diagram illustrating a graph depictingthe net interaction energy curve formed when subtracting the attractioncurve from the repulsion curve in accordance with one embodiment of theinvention.

FIG. 5 is a simplified schematic diagram illustrating an aggregate ofsurfactant molecules, which may form the solid particles describedherein, in accordance with one embodiment of the invention.

FIG. 6A is a simplified schematic diagram of a top view of a system forcleaning a substrate in accordance with one embodiment of the invention.

FIG. 6B is a simplified schematic diagram of a side view of the systemdepicted in FIG. 6A for cleaning a substrate in accordance with oneembodiment of the invention.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the present invention. Itwill be apparent, however, to one skilled in the art that the presentinvention may be practiced without some or all of these specificdetails. In other instances, well known process operations have not beendescribed in detail in order not to unnecessarily obscure the presentinvention.

The embodiments described herein provide for a cleaning technique thateliminates the need for abrasive contact and is efficient at cleaningcontaminants from semiconductor substrates, some of which may containhigh aspect ratio features. While the embodiments provide specificexamples related to semiconductor cleaning applications, these cleaningapplications may be extended to any technology requiring the removal ofcontaminants from a substrate. As described below, a cleaning solutionhaving a continuous phase and a dispersed phase is provided. Solidparticles are disseminated throughout the continuous phase. As usedherein, the dispersed phase refers to either gas bubbles dispersedthroughout the continuous phase, e.g., with reference to a foam, orliquid droplets dispersed throughout the continuous phase, e.g. withreference to an emulsion, or even solids (different than the solidparticles) dispersed through the continuous phase. In one embodiment,the dispersed phase provides a vehicle to bring the solid particlesproximate to the contaminant in order for the solid particles and thecontaminant to interact to eventually remove the contaminant.

FIG. 1 is an illustration showing a physical diagram of a cleaningmaterial 101 for removing contamination 103 from a semiconductor wafer(“wafer”) 105, in accordance with one embodiment of the presentinvention. The cleaning material 101 of the present invention includes acontinuous liquid medium 107, solid components 109, and immisciblecomponents 111. The solid components 109 and immiscible components 111are dispersed within the continuous liquid medium 107. In variousembodiments, the continuous liquid medium 107 can be either aqueous ornon-aqueous. Depending on the particular embodiment, the immisciblecomponents 111 can be defined in either a gas phase, a liquid phase, asolid phase, or a combination of gas, liquid, and solid phases. In oneembodiment, the immiscible components 111 are defined as a mixture ofimmiscible components 111, wherein each immiscible component 111 withinthe mixture has either a common physical state or a different physicalstate. For example, in various embodiments the physical states ofimmiscible components 111 within the mixture of immiscible components111 can include a gas and a liquid, a gas and a solid, a liquid and asolid, or any combination of multiple gases, multiple liquids, andmultiple solids.

It should be appreciated that the immiscible components 111 areimmiscible with respect to the continuous liquid medium 107. In oneexemplary embodiment, the immiscible components 111 are defined as gasbubbles within the continuous liquid medium 107. In another exemplaryembodiment, the immiscible components 111 are defined as liquid dropletswithin the continuous liquid medium 107. Regardless of the particularembodiment associated with the continuous liquid medium 107 andimmiscible components 111, the solid components 109 are dispersed insuspension within the continuous liquid medium 107.

It should be understood that depending on the particular embodiment, thesolid components 109 within the cleaning material 101 may possessphysical properties representing essentially any sub-state within thesolid phase, wherein the solid phase is defined as a phase other thanliquid or gas. For example, physical properties such as elasticity andplasticity can vary among different types of solid components 109 withinthe cleaning material 101. Additionally, it should be understood that invarious embodiments the solid components 109 can be defined ascrystalline solids or non-crystalline solids. Regardless of theirparticular physical properties, the solid components 109 within thecleaning material 101 should be capable of avoiding adherence to thesurface of wafer 105 when positioned in either close proximity to orcontact with the surface of wafer 105. Additionally, the mechanicalproperties of the solid components 109 should not cause damage to thewafer 105 surface during the cleaning process. Furthermore, the solidcomponents 109 should be capable of establishing an interaction with thecontaminant 103 material present on the wafer 105 surface whenpositioned in either close proximity or contact with the contaminant103. For example, the size and shape of the solid components 109 shouldbe favorable for establishing the interaction between the solidcomponents 109 and the contaminants 103.

The solid components 109 within the cleaning material 101 should becapable of interacting with contaminants 103 on the wafer 105 whileavoiding both adhesion and damage to the wafer 105. In addition, thesolid components 109 should avoid dissolution in the liquid medium 107and should have a surface functionality that enables dispersionthroughout the liquid medium 107. For solid components 109 that do nothave surface functionality that enables dispersion throughout the liquidmedium 107, chemical dispersants may be added to the liquid medium 107to enable dispersion of the solid components 109. Depending on theirspecific chemical characteristics and their interaction with thesurrounding liquid medium 107, the solid components 109 may take one ormore of several different forms. For example, in various embodiments thesolid components 109 may form aggregates, colloids, gels, coalescedspheres, or essentially any other type of agglutination, coagulation,flocculation, agglomeration, or coalescence. It should be appreciatedthat the exemplary list solid component 109 forms identified above isnot intended to represent an inclusive list. In other embodiments, thesolid components 109 may take a form not specifically identified herein.Therefore, the point to understand is that the solid components 109 canbe defined as essentially any solid material capable of functioning inthe manner previously described with respect to their interaction withthe wafer 105 and the contaminants 103.

Some exemplary solid components 109 include aliphatic acids, carboxylicacids, paraffin, wax, polymers, polystyrene, polypeptides, and othervisco-elastic materials. The solid component 109 material should bepresent at a concentration that exceeds its solubility limit within theliquid medium 107. In addition, it should be understood that thecleaning effectiveness associated with a particular solid component 109material may vary as a function of temperature, pH, and otherenvironmental conditions.

The aliphatic acids represent essentially any acid defined by organiccompounds in which carbon atoms form open chains. A fatty acid is anexample of an aliphatic acid that can be used as the solid components109 within the cleaning material 101. Examples of fatty acids that maybe used as the solid components 109 include lauric, palmtic, stearic,oleic, linoleic, linolenic, arachidonic, gadoleic, eurcic, butyric,caproic, caprylic, myristic, margaric, behenic, lignoceric, myristoleic,palmitoleic, nervanic, parinaric, timnodonic, brassic, clupanodonicacid, lignoceric acid, cerotic acid, and mixtures thereof, among others.In one embodiment, the solid components 109 can represent a mixture offatty acids defined by various carbon chain lengths extending from C-1to about C-26. Carboxylic acids are defined by essentially any organicacid that includes one or more carboxyl groups (COOH). When used as thesolid components 109, the carboxylic acids can include mixtures ofvarious carbon chain lengths extending from C-1 through about C-100.Also, the carboxylic acids can include other functional groups such asbut not limited to methyl, vinyl, alkyne, amide, primary amine,secondary amine, tertiary amine, azo, nitrile, nitro, nitroso, pyridyl,carboxyl, peroxy, aldehyde, ketone, primary imine, secondary imine,ether, ester, halogen, isocyanate, isothiocyanate, phenyl, benzyl,phosphodiester, sulfhydryl, but still maintaining insolubility in theliquid medium 107.

In some embodiments, addition of a dispersant material to the liquidmedium 107 may be required to enable a particular type of solidcomponent 109, such as a fatty acid, to disperse throughout the liquidmedium 107. For example, a base can be added to the liquid medium 107 toenable suspension of solid components 109 formed from materials such ascarboxylic acid or stearic acid that are present in less thanstoichiometric quantities. In one embodiment, the base is AmmoniumHydroxide, however, any commercially available base may be used with theembodiments described herein. Additionally, the surface functionality ofthe solid component 109 materials can be influenced by the inclusion ofmoieties that are miscible with the liquid medium 107, such ascarboxylate, phosphate, sulfate groups, polyol groups, ethylene oxide,etc. The point to be understood is that the solid components 109 shouldbe dispersible in a substantially uniform manner throughout the liquidmedium 107 such that the solid components 109 avoid clumping togetherinto a form that cannot be forced to interact with the contaminants 103present on the wafer 105.

As previously mentioned, the continuous liquid medium 107 can be eitheraqueous or non-aqueous. For example, an aqueous liquid medium 107 can bedefined by de-ionized water in one embodiment. In another embodiment, anon-aqueous liquid medium 107 can be defined by a hydrocarbon, afluorocarbon, a mineral oil, or an alcohol, among others. Irrespectiveof whether the liquid medium 107 is aqueous or non-aqueous, it should beunderstood that the liquid medium 107 can be modified to include ionicor non-ionic solvents and other chemical additives. For example, thechemical additives to the liquid medium 107 can include any combinationof co-solvents, pH modifiers, chelating agents, polar solvents,surfactants, ammonia hydroxide, hydrogen peroxide, hydrofluoric acid,tetramethylammonium hydroxide, and rheology modifiers such as polymers,particulates, and polypeptides.

As previously mentioned, the immiscible components 111 within thecleaning material 101 can be defined in either the gas phase, the liquidphase, the solid phase, or a combination thereof. In the embodimenthaving the immiscible components 111 defined in the gas phase, theimmiscible components 111 are defined as gas bubbles dispersedthroughout the continuous liquid medium 107. In one embodiment, the gasbubbles are defined to occupy 5% to 99.9% of the cleaning material 101by volume. In another embodiment, the gas bubbles are defined to occupy50% to 95% of the cleaning material 101 by weight. The gas defining theimmiscible components 111 can be either inert, e.g., N₂, Ar, etc., orreactive, e.g., O₂, O₃, H₂O₂, air, H₂, NH₃, HF, etc.

In the embodiment having the immiscible components 111 defined in theliquid phase, the immiscible components 111 are defined as liquiddroplets dispersed throughout the continuous liquid medium 107, whereinthe liquid droplets are immiscible within the liquid medium 107. Theliquid defining the immiscible components 111 can be either inert orreactive. For example, a low-molecular weight alkane, e.g., pentane,hexane, heptane, octane, nonane, decane, or mineral oil may be used asan inert liquid for defining the immiscible components 111, wherein theliquid medium 107 is aqueous. In another example, oil soluble surfacemodifiers may be used as a reactive liquid for defining the immisciblecomponents 111.

During the cleaning process, a downward force is exerted on the solidcomponents 109 within the liquid medium 107 such that the solidcomponents 109 are brought within close proximity or contact with thecontaminants 103 on the wafer 105. The immiscible components 111 withinthe cleaning material 101 provide the mechanism by which the downwardforce is exerted on the solid components 109. When the solid component109 is forced within sufficient proximity to or contact with thecontaminant 103, an interaction is established between the solidcomponent 109 and the contaminant 103. The interaction between the solidcomponent 109 and the contaminant 103 is sufficient to overcome anadhesive force between the contaminant 103 and the wafer 105, as well asany repulsive forces between the solid component 109 and thecontaminant. Therefore, when the solid component 109 is moved away fromthe wafer 105, the contaminant 103 that interacted with the solidcomponent 109 is also moved away from the wafer 105, i.e., thecontaminant 103 is cleaned from the wafer 105.

FIGS. 2A-2B are illustrations showing how the cleaning material 101functions to remove the contaminant 103 from the wafer 105, inaccordance with one embodiment of the present invention. It should beunderstood that the cleaning material 101 depicted in FIGS. 2A-2Bpossesses the same characteristics as previously described with respectto FIG. 1. As shown in FIG. 2A, within the liquid medium 107 of thecleaning material 101, the solid component 109 is interposed between thecontaminant 103 and the immiscible component 111. The immisciblecomponent 111 within the liquid medium 107, whether gas bubbles orliquid droplets, has an associated surface tension. Therefore, when theimmiscible component 111 is pressed downward against the solid component109, the immiscible component 111 becomes deformed and exerts a downwardforce (F) on the solid component 109. This downward force (F), or anormal component of F, serves to move the solid component 109 toward thewafer 105 and contaminant 103 thereon. In one embodiment, theinteraction between the solid component 109 and contaminant 103 occurswhen the solid component 109 is forced sufficiently close to thecontaminant 103. In one embodiment, this distance may be within about 10nanometers. In another embodiment, the interaction between the solidcomponent 109 and contaminant 103 occurs when the solid component 109actually contacts the contaminant 103. This interaction may also bereferred to as solid component 109 engaging contaminant 103.

The interaction force between the solid component 109 and thecontaminant 103 is stronger than the force connecting the contaminant103 to the wafer 105. Additionally, in an embodiment where the solidcomponent 109 binds with the contaminant 103, a force used to move thesolid component 109 away from the wafer 105 is stronger than the forceconnecting the contaminant 103 to the wafer 105. Therefore, as depictedin FIG. 2B, when the solid component 109 is moved away from the wafer105, the contaminant 103 bound to the solid component 109 is also movedaway from the wafer 105. It should be appreciated that because the solidcomponents 109 interact with the contamination 103 to affect thecleaning process, contamination 103 removal across the wafer 105 will bedependent on how well the solid components 109 are distributed acrossthe wafer 105. In a preferred embodiment, the solid components 109 willbe so well distributed that essentially every contaminant 103 on thewafer 105 will be in proximity to at least one solid component 109. Itshould also be appreciated that one solid component 109 may come incontact with or interact with more than one contaminant 103, either in asimultaneous manner or in a sequential manner. Furthermore, solidcomponent 109 may be a mixture of different components as opposed to allthe same component. Thus, the cleaning solution is capable of beingdesigned for a specific purpose, i.e., targeting a specific contaminant,or the cleaning solution can have a broad spectrum of contaminanttargets where multiple solid components are provided.

Interaction between the solid component 109 and the contaminant 103 canbe established through one or more mechanisms including adhesion,collision, and attractive forces, among others. Adhesion between thesolid component 109 and contaminant 103 can be established throughchemical interaction and/or physical interaction. For example, in oneembodiment, chemical interaction causes a glue-like effect to occurbetween the solid component 109 and the contaminant 103. In anotherembodiment, physical interaction between the solid component 109 and thecontaminant 103 is facilitated by the mechanical properties of the solidcomponent 109. For example, the solid component 109 can be malleablesuch that when pressed against the contaminant 103, the contaminant 103becomes imprinted within the malleable solid component 109. In anotherembodiment, the contaminant 103 can become entangled in a network ofsolid components 109. In this embodiment, mechanical stresses can betransferred through the network of solid components 109 to thecontaminant 103, thus providing the mechanical force necessary forremoval of the contaminant 103 from the wafer 105.

Deformation of the solid component 109 due to imprinting by thecontaminant 103 creates a mechanical linkage between the solid component109 and the contaminant 103. For example, a surface topography of thecontaminant 103 may be such that as the contaminant 103 is pressed intothe solid component 109, portions of the solid component 109 materialenters regions within the surface topography of the contaminant 103 fromwhich the solid component 109 material cannot easily escape, therebycreating a locking mechanism. Additionally, as the contaminant 103 ispressed into the solid component 109, a vacuum force can be establishedto resist removal of the contaminant 103 from the solid component 109.

In another embodiment, energy transferred from the solid component 109to the contaminant 103 through direct or indirect contact may cause thecontaminant 103 to be dislodged from the wafer 105. In this embodiment,the solid component 109 may be softer or harder than the contaminant103. If the solid component 109 is softer than the contaminant 103,greater deformation of the solid component 109 is likely to occur duringthe collision, resulting in less transfer of kinetic energy fordislodging the contaminant 103 from the wafer 105. However, in the casewhere the solid component 109 is softer than the contaminant 103, theadhesive connection between the solid component 109 and the contaminant103 may be stronger. Conversely, if the solid component 109 is at leastas hard as the contaminant 103, a substantially complete transfer ofenergy can occur between the solid component 109 and the contaminant103, thus increasing the force that serves to dislodge the contaminant103 from the wafer 105. However, in the case where the solid component109 is at least as hard as the contaminant 103, interaction forces thatrely on deformation of the solid component 109 may be reduced. It shouldbe appreciated that physical properties and relative velocitiesassociated with the solid component 109 and the contaminant 103 willinfluence the collision interaction there between.

In addition to the foregoing, in one embodiment, interaction between thesolid component 109 and contaminant 103 can result from electrostaticattraction. For example, if the solid component 109 and the contaminant103 have opposite surface charges they will be electrically attracted toeach other. It is possible that the electrostatic attraction between thesolid component 109 and the contaminant 103 can be sufficient toovercome the force connecting the contaminant 103 to the wafer 105.

In another embodiment, an electrostatic repulsion may exist between thesolid component 109 and the contaminant 103. For example, both the solidcomponent 109 and the contaminant 103 can have either a negative surfacecharge or a positive surface charge. If the solid component 109 and thecontaminant 103 can be brought into close enough proximity, theelectrostatic repulsion there between can be overcome through van derWaals attraction. The force applied by the immiscible component 111 tothe solid component 109 may be sufficient to overcome the electrostaticrepulsion such that van der Waals attractive forces are establishedbetween the solid component 109 and the contaminant 103. Further detailsof this embodiment, are provided with reference to FIG. 4. Additionally,in another embodiment, the pH of the liquid medium 107 can be adjustedto compensate for surface charges present on one or both of the solidcomponent 109 and contaminant 103, such that the electrostatic repulsionthere between is reduced to facilitate interaction, or so that eitherthe solid component or the contamination exhibit surface charge reversalrelative to the other resulting in electrostatic attraction.

FIG. 3 is an illustration showing a flowchart of a method for removingcontamination from a substrate, in accordance with one embodiment of thepresent invention. It should be understood that the substrate referencedin the method of FIG. 3 can represent a semiconductor wafer or any othertype of substrate from which contaminants associated with asemiconductor fabrication process need to be removed. Also, thecontaminants referenced in the method of FIG. 3 can representessentially any type of contaminant associated with the semiconductorwafer fabrication process, including but not limited to particulatecontamination, trace metal contamination, organic contamination,photoresist debris, contamination from wafer handling equipment, andwafer backside particulate contamination.

The method of FIG. 3 includes an operation 301 for disposing a cleaningmaterial over a substrate, wherein the cleaning material includes solidcomponents dispersed within a liquid medium. The cleaning materialreferenced in the method of FIG. 3 is the same as previously describedwith respect to FIGS. 1, 2A, and 2B. Therefore, the solid componentswithin the cleaning material are dispersed in suspension within theliquid medium. Also, the solid components are defined to avoid damagingthe substrate and to avoid adherence to the substrate. In oneembodiment, the solid components are defined as crystalline solids. Inanother embodiment, the solid components are defined as non-crystallinesolids. In yet another embodiment, the solid components are representedas a combination of crystalline and non-crystalline solids.Additionally, in various embodiments, the liquid medium can be eitheraqueous or non-aqueous.

The method also includes an operation 303 for applying a force to asolid component to bring the solid component within proximity to acontaminant present on the substrate, such that an interaction isestablished between the solid component and the contaminant. Aspreviously discussed, immiscible components are provided within thecleaning material to apply the force to the solid component necessary tobring the solid component within proximity to the contaminant. In oneembodiment, the method can include an operation for controlling theimmiscible components to apply a controlled amount of force to the solidcomponent. The immiscible components can be defined as gas bubbles orimmiscible liquid droplets within the liquid medium. Additionally, theimmiscible components can be represented as a combination of gas bubblesand immiscible liquid droplets within the liquid medium.

In one embodiment of the method, the immiscible components are definedwithin the liquid medium prior to disposing the cleaning material overthe substrate. However, in another embodiment, the method can include anoperation to form the immiscible components in-situ followingdisposition of the cleaning material over the substrate. For example,the immiscible components can be formed from a dissolved gas within theliquid medium upon a decrease in ambient pressure relative to thecleaning material. It should be appreciated that formation of theimmiscible components in situ may enhance the contamination removalprocess. For example, in one embodiment, gravity serves to pull thesolid components toward the substrate prior to formation of theimmiscible components. Then, the ambient pressure is reduced such thatgas previously dissolved within the liquid medium comes out of solutionto form gas bubbles. Because the solid components have settled bygravity toward the substrate, the majority of gas bubbles will formabove the solid components. Formation of the gas bubbles above the solidcomponents, with the solid components already settled toward thesubstrate, will serve to enhance movement of the solid components towithin proximity of the contaminants on the substrate.

In various embodiments, the interaction between the solid component andthe contaminant can be established by adhesive forces, collision forces,attractive forces, or a combination thereof. Also, in one embodiment,the method can include an operation for modifying a chemistry of theliquid medium to enhance interaction between the solid component and thecontaminant. For example, the pH of the liquid medium can be modified tocancel surface charges on one or both of the solid component andcontaminant such that electrostatic repulsion is reduced.

Additionally, in one embodiment, the method can include an operation forcontrolling a temperature of the cleaning material to enhanceinteraction between the solid component and the contaminant. Morespecifically, the temperature of the cleaning material can be controlledto control the properties of the solid component. For example, at ahigher temperature the solid component may be more malleable such thatit conforms better when pressed against the contaminant. Then, once thesolid component is pressed and conformed to the contaminant, thetemperature is lowered to make the solid component less malleable tobetter hold its conformal shape relative to the contaminant, thuseffectively locking the solid component and contaminant together. Thetemperature may also be used to control the solubility and therefore theconcentration of the solid components. For example, at highertemperatures the solid component may be more likely to dissolve in theliquid medium. The temperature may also be used to control and/or enableformation of solid components in-situ on the wafer from liquid-liquidsuspension.

In a separate embodiment, the method can include an operation forprecipitating solids dissolved within the continuous liquid medium. Thisprecipitation operation can be accomplished by dissolving the solidsinto a solvent and then adding a component that is miscible with thesolvent but that does not dissolve the solid. Addition of the componentthat is miscible with the solvent but that does not dissolve the solidcauses the precipitation of a solid component.

The method further includes an operation 305 for moving the solidcomponent away from the substrate such that the contaminant thatinteracted with the solid component is removed from the substrate. Inone embodiment, the method includes an operation for controlling a flowrate of the cleaning material over the substrate to control or enhancemovement of the solid component and/or contaminant away from thesubstrate. The method of the present invention for removingcontamination from a substrate can be implemented in many different waysso long as there is a means for applying a force to the solid componentsof the cleaning material such that the solid components establish aninteraction with the contaminants to be removed.

FIG. 4 is a simplified schematic diagram illustrating a graph depictingthe net interaction energy curve fowled when subtracting the attractioncurve from the repulsion curve in accordance with one embodiment of theinvention. As illustrated in FIG. 4 electrical repulsion is depicted byline 401 while Van der Waals attraction is depicted by line 403. TheY-axis represents energy with repulsive energy being shown above theX-axis and attractive energy illustrated below the X-axis. The X-axisrepresents distance between particles. The net interaction energy isdepicted by curve 405 and is simply the sum of lines 401 and 403. Region407 may be referred to as an energy trap, while region 409 may bereferred to as an energy barrier. One skilled in the art will appreciatethat electrostatic repulsion becomes significant when twoparticles/colloids approach each other and their double layers begin tointerfere. Energy is required to overcome this repulsion. In oneembodiment described herein, this energy may be provided by the cleaningsolution, or more specifically, an immiscible component of the cleaningsolution, as described above. The electrostatic repulsion curve 401indicates the energy that must be overcome if the particles are to beforced together. It should be appreciated that the maximum energy isrelated to the surface potential and the zeta potential.

Van der Waals attraction is actually the result of forces betweenindividual molecules in each particle/colloid. The effect is additive;that is, one molecule of the first particle/colloid has a Van der Waalsattraction to each molecule in the second colloid. This is repeated foreach molecule in the first particle/colloid, and the total force is thesum of all of these. The attractive energy curve 403 is used to indicatethe variation in Van der Walls force with distance between theparticles. At each distance on the X axis the smaller value issubtracted from the larger value to get the net energy. The net value isthen plotted, above if repulsive and below if attractive, and a curve isformed. If there is a repulsive section, then the point of maximumrepulsive energy is called the energy barrier 409. The height of energybarrier 409 indicates how stable the system is. In order to agglomerate,two particles on a collision course must have sufficient kinetic energydue to their velocity mass to jump over this barrier. If the barrier iscleared, then the net interaction is all attractive and as a result, theparticles agglomerate. This inner region 407 is referred to as an energytrap since the particles/colloids can be considered to be trappedtogether by Van der Waals forces. One skilled in the art will appreciatethat the environmental conditions for a colloidal solution may bealtered to either increase or decrease the energy barrier, depending onthe particular application. The conditions that can be altered includechanging ionic strength, changing pH, or adding surface-active materialsto directly affect the charge of the colloid. In each case, zetapotential measurements can indicate the impact of the alternation onoverall stability.

FIG. 5 is a simplified schematic diagram illustrating anaggregate/assembly of surfactant molecules, which may form the solidparticles described herein, in accordance with one embodiment of theinvention. Typically the aggregate/assembly of surfactant molecules, isusually of a globular shape, but other geometrical shapes are alsopossible, e.g., ellipsoid, cylinder, vesicles, lamellae, etc. Oneskilled in the art will appreciate that the aggregate/assembly ofsurfactant molecules may also be referred to a micelle. Micelles formwhen a concentration of surfactant is greater than the critical micellarconcentration (CMC), and the temperature of the system is greater thanthe critical micellar temperature. As is generally known surfactants arechemicals that contain both hydrophobic groups, e.g. long hydrocarbonchains, and hydrophilic groups, e.g., ionic or polar groups. Thus, in anaqueous or other polar solvent, the core 501 of the micelle consists ofthe hydrophobic portion of the molecules, while the hydrophilic portions503 remain on the surface of the molecule so that they can maintainfavorable contact with water. In the case of ionic surfactants, in oneembodiment, the electric charge of the ionic heads is neutralized by theoppositely charged ions (counter ions) located in the layer around themicelle, to fulfill the condition of electroneutrality. In an alternateembodiment, where a non-polar solvent is used in the continuous phase,the hydrophilic groups will form the core of the micelle, and thehydrophobic groups remain on the surface of the micelle, i.e. a reversemicelle. Thus, in one embodiment, the micelle 109 represents anagglomeration/assembly of surface-active molecules that may function asthe solid components 109. Of course, it should be understood that thisis just one exemplary embodiment and that solid components may be formedthrough other techniques mentioned above.

Described below are exemplary techniques for manufacturing the cleaningsolution. It should be appreciated that these are exemplary techniquesdirected at the use of stearic acid with an aqueous continuous phasethat may be combined into a foam application or an emulsion application.Example 1 provides a technique requiring melting of the fatty acid andExample 2 pre-mills the fatty acid to achieve a desirable particledistribution, thereby eliminating the need to melt the fatty acid.Example 3 provides a technique where dissolved fatty acids areprecipitated from a solvent to achieve a desirable particledistribution. Of course, numerous other techniques may be utilized tomanufacture the cleaning solution and different fatty acids may be used.In addition, a non-polar solvent may be used in place of water and anon-polar or a polar compound may be mixed/dissolved in the non-polarsolvent.

Example 1

Water is heated to above 70 degrees Celsius (the melting point ofStearic acid). Solid Stearic acid (about 0.1% by weight to about 10% byweight) is heated above 70 degrees Celsius and added to the heatedwater. The water-stearic acid mixture is stirred at a rate so that theimmiscible stearic acid is dispersed or emulsified within the continuouswater phase. Ionization of the stearic acid is initiated by adding abase to bring the pH up to a point where about 50% of the carboxylicacid is dissociated, i.e., the dissociation constant (pK_(a)) is about50%. This occurs at a pH of about 10.2. An exemplary base added to thesolution to bring the pH up is ammonium hydroxide (NH₄OH). Theconcentration of the NH₄OH can range between 0.25% and 10% by weight.The stearic acid/water/NH₄OH mixture is stirred for an additional 20minutes to form a homogeneous solution. The solution cools to ambientand sits for 10 hours and over time a precipitate forms, i.e., the solidcomponents. During stirring, air can be entrained into the mixture butit is not necessary. The size distribution of these precipitateparticles (solid components) is between about 50 nanometers and 5000micrometers.

Example 2

The granular stearic acid is milled to a particle size distributionbetween about 0.5 and about 5000 micrometers. Any commercially availablepowder mill may achieve this size distribution. The milled Stearic acid(about 0.1% by weight to about 10% by weight) in granular form is addedto water while agitating the solution. The solution can be agitated byshaking, stirring, rotating, etc. Dissociation of the stearic acid isinitiated by adding a base to bring the pH up to a point where about 50%of the carboxylic acid is dissociated, i.e., the pK_(a) is about 50%.This occurs at a pH of above 10.2. An exemplary base added to thesolution to bring the pH up is ammonium hydroxide (NH₄OH). Theconcentration of the NH₄OH can range between 0.5% and 10% by weight.Adding NH₄OH to the aqueous solution while agitating the solutiondisperses the solid stearic acid component into the continuous waterphase. The ionized solid stearic acid component remains suspended withinthe continuous aqueous phase without agitation. The size distribution ofthese particles is between about 0.5 and about 5,000 micrometers.

Example 3

A mixture of stearic and palmitic acids is dissolved in isopropanol(IPA) while agitating the solution. The concentration of dissolved fattyacids in the solvent can range from about 2% to 20% by weight. Heatingof the solvent below the boiling point of the solvent or addition ofanother organic solvent or solvents, such as acetone or benzene, canimprove solubility of the fatty acid. The solution can be agitated byshaking, stirring, rotating, etc. Once the dissolution is complete, theremaining solids can be removed by filtration or centrifugation. Thesolid-free solution is next mixed with water (a non-solvent for thefatty acid) to precipitate a fatty-acid solid. The precipitated fattyacid becomes suspended in solution with the size distribution in therange between 0.5 and 5,000 microns. Ionization of the stearic acid canbe initiated by adding a base to bring the pH up to 10.2 or higher. Anexemplary base added to the solution to bring the pH up is ammoniumhydroxide (NH₄OH). The concentration of the NH₄OH can range between0.25% and 10% by weight.

FIG. 6A is a simplified schematic diagram of a top view of a system forcleaning a substrate in accordance with one embodiment of the invention.Substrate 601 moves in a linear direction toward the cleaning head. Thecleaning head includes a portion 603 configured to provide the cleaningsolution. As described above, the cleaning solution may be in the formof a foam or an emulsion. In one embodiment, the cleaning solution isdelivered from a reservoir, which may or may not be pressurized. If thereservoir is pressurized, the cleaning solution may be aerated anddevelop into a foam prior to being delivered to the cleaning head. Wherethe reservoir is not pressurized, the cleaning solution may be pumped ordelivered through other commonly known means. In another embodiment, anemulsion may be delivered to the cleaning head from an off-linereservoir. Portion 605 includes a rinse chemistry, such as deionizedwater (DIW) or some other cleaning chemistry commonly used for theparticular application. Portion 607 of the cleaning head provides thedrying capability and may utilize an inert gas, such as Nitrogen and/ora low vapor pressure liquid such as isopropyl alcohol (IPA). It shouldbe appreciated that portions 605 and 607, which are located downstreamfrom the cleaning portion 603 in one embodiment, may provide a cleaningmeniscus and may be the proximity cleaning head owned by the assigneeand further described in the cross referenced applications listed below.One skilled in the art will appreciate that substrate 601 may rotateand/or rotate and move linearly. Alternatively, the cleaning head maymove over substrate 601 while the substrate is stationary or alsomoving. In yet another embodiment, the cleaning may be performed in acleaning compartment where a single wafer is deposited and the cleaningsolution is applied. In still yet another embodiment, a tool providingsequential compartments for each of portion 603, 605, and 607 may beprovided. In another embodiment, the cleaning head may include twoportions 603 for cleaning solution with portion 605 sandwiched inbetween the two portions 603. Thus, numerous configurations areavailable for the functionality described herein.

FIG. 6B is a side view of the cleaning head of FIG. 6A. Cleaning fluidis supplied to portion 603 as mentioned above. DIW and/or some othersuitable cleaning chemistry may be provided to portion 605. Vacuum mayoptionally be provided to portion 605 also to provide a meniscus asdiscussed in the cross-referenced application below in more detail. Aninert gas and/or IPA are provided to portion 607. Here again, whileFIGS. 6A and 6B are illustrated with respect to a semiconductorsubstrate, the embodiments may be extended to flat panel displays, solarcells, memory devices, etc.

For additional information about the proximity vapor clean and drysystem, reference can be made to an exemplary system described in theU.S. Pat. No. 6,488,040, issued on Dec. 3, 2002 and entitled “CAPILLARYPROXIMITY HEADS FOR SINGLE WAFER CLEANING AND DRYING.” This U.S. patentapplication, which is assigned to Lam Research Corporation, the assigneeof the subject application, is incorporated herein by reference.

For additional information with respect to the proximity head, referencecan be made to an exemplary proximity head, as described in the U.S.Pat. No. 6,616,772, issued on Sep. 9, 2003 and entitled “METHODS FORWAFER PROXIMITY CLEANING AND DRYING.” This U.S. patent application,which is assigned to Lam Research Corporation, the assignee of thesubject application, is incorporated herein by reference.

For additional information about top and bottom menisci, reference canbe made to the exemplary meniscus, as disclosed in U.S. patentapplication Ser. No. 10/330,843, filed on Dec. 24, 2002 and entitled“MENISCUS, VACUUM, IPA VAPOR, DRYING MANIFOLD.” This U.S. patentapplication, which is assigned to Lam Research Corporation, the assigneeof the subject application, is incorporated herein by reference.

For additional information about menisci, reference can be made to U.S.Pat. No. 6,998,327, issued on Jan. 24, 2005 and entitled “METHODS ANDSYSTEMS FOR PROCESSING A SUBSTRATE USING A DYNAMIC LIQUID MENISCUS,” andU.S. Pat. No. 6,998,326, issued on Jan. 24, 2005 and entitled “PHOBICBARRIER MENISCUS SEPARATION AND CONTAINMENT.” These U.S. patents, whichare assigned to the assignee of the subject application, areincorporated herein by reference in their entirety for all purposes

In some contemplated embodiments, the continuous phase or dispersantphase includes those compounds that are considered part of thehydrocarbon family. Hydrocarbon compounds are those compounds thatcomprise carbon and hydrogen. It should be understood that a majority ofhydrocarbon compounds are non-polar, and therefore less polar thanwater; however, there are a few hydrocarbon compounds that could beconsidered to be as polar or more polar than water. Hydrocarboncompounds are generally broken down into three classes: aliphatic,cyclic and aromatic. Aliphatic hydrocarbon compounds may comprise bothstraight-chain compounds and compounds that are branched and possiblycross-linked, however, aliphatic hydrocarbon compounds are notconsidered cyclic. Cyclic hydrocarbon compounds are those compounds thatcomprise at least three carbon atoms oriented in a ring structure withproperties similar to aliphatic hydrocarbon compounds. Aromatichydrocarbon solvents are those compounds that comprise generally threeor more unsaturated bonds with a single ring or multiple rings attachedby a common bond and/or multiple rings fused together. Contemplatedhydrocarbon compounds include toluene, xylene, p-xylene, m-xylene,mesitylene, solvent naphtha H, solvent naphtha A, alkanes, such aspentane, hexane, isohexane, heptane, nonane, octane, dodecane,2-methylbutane, hexadecane, tridecane, pentadecane, cyclopentane,2,2,4-trimethylpentane, petroleum ethers, halogenated hydrocarbons, suchas chlorinated hydrocarbons, fluorinated hydrocarbons, nitratedhydrocarbons, benzene, 1,2-dimethylbenzene, 1,2,4-trimethylbenzene,mineral spirits, kerosine, isobutylbenzene, methylnaphthalene,ethyltoluene, ligroine. Particularly contemplated solvents include, butare not limited to, pentane, hexane, heptane, cyclohexane, benzene,toluene, xylene and mixtures or combinations thereof.

In other contemplated embodiments, the continuous phase or dispersantphase may comprise those compounds that are not considered part of thehydrocarbon family of compounds, such as ketones, which includefluorinated ketones, e.g., acetone, diethyl ketone, methyl ethyl ketoneand the like, alcohols, which include fluorinated alcohols, esters,which include fluorinated esters, fluorinated and non-fluorinatedcarbonate-based compounds, such as propylene carbonate and the like,ethers, which include fluorinated ethers, and amines, which includefluorinated amines. In yet other contemplated embodiments, thecontinuous phase or dispersant phase may comprise a combination of anyof the compounds mentioned herein. Thus, where the continuous phase is apolar solvent such as water, the above listed non-polar compounds may beused in the dispersed phase, as the non-polar compounds are typicallyimmiscible with polar solvents. Of course, the non-polar compounds maybe used in the continuous phase for certain applications and the polarcompounds may be used for the dispersed phase. Exemplary polar solventsbesides water include acetic acid, formic acid, methanol, ethanol,n-propanol, n-butanol, isopropanol, acetone, acetonitrile,dimethylformamide, dimethyl sulfoxide, and mixtures thereof. It shouldbe appreciate that the lists of materials provided herein are meant tobe exemplary and not limiting.

Although the present invention has been described in the context ofremoving contaminants from a semiconductor wafer, it should beunderstood that the previously described principles and techniques ofthe present invention can be equally applied to cleaning surfaces otherthan semiconductor wafers. For example, the present invention can beused to clean any equipment surface used in semiconductor manufacturing,wherein any equipment surface refers to any surface that is inenvironmental communication with the wafer, e.g., shares air space withthe wafer. The present invention can also be used in other technologyareas where contamination removal is important. For example, the presentinvention can be used to remove contamination on parts used in the spaceprogram, or other high technology areas such as surface science, energy,optics, microelectronics, MEMS, flat-panel processing, solar cells,memory devices, etc. It should be understood that the aforementionedlisting of exemplary areas where the present invention may be used isnot intended to represent an inclusive listing. Furthermore, it shouldbe appreciated that the wafer as used in the exemplary descriptionherein can be generalized to represent essentially any other structure,such as a substrate, a part, a panel, etc.

While this invention has been described in terms of several embodiments,it will be appreciated that those skilled in the art upon reading thepreceding specifications and studying the drawings will realize variousalterations, additions, permutations and equivalents thereof. Therefore,it is intended that the present invention includes all such alterations,additions, permutations, and equivalents as fall within the true spiritand scope of the invention. In the claims, elements and/or steps do notimply any particular order of operation, unless explicitly stated in theclaims.

1. A system for cleaning a substrate, comprising: a cleaning headconfigured to be disposed over a surface of the substrate, the cleaninghead including a cleaning portion; and a cleaning solution reservoirconnected to supply a cleaning solution to the cleaning portion of thecleaning head, the cleaning solution including a first immiscible liquidcombined with a second immiscible liquid, the second immiscible liquidforming a plurality of droplets dispersed within the first immiscibleliquid, the cleaning solution further including solid particlesdistributed within the first immiscible liquid, wherein the cleaningportion of the cleaning head is structured to apply the cleaningsolution to the surface of the substrate so as to direct the pluralityof droplets of the second immiscible liquid to apply a force from someof the plurality of droplets to some of the solid particles, wherebysome of the solid particles adhere to one or more contaminants presenton the surface of the substrate under the applied force.
 2. The systemof claim 1, wherein the cleaning head includes a rinsing portion and adrying portion downstream from the cleaning portion.
 3. The system ofclaim 1, wherein the cleaning solution is stored under pressure in asingle physical state in the cleaning solution reservoir and deliveredat atmospheric pressure in multiple physical states to the cleaningportion of the cleaning head.
 4. The system of claim 1, wherein thecleaning head is stationary.
 5. The system of claim 1, wherein thecleaning head is moveable relative to the substrate.
 6. The system ofclaim 1, wherein the cleaning head includes at least two of the cleaningportion, and wherein the cleaning solution reservoir is connected tosupply the cleaning solution to each of the at least two of the cleaningportion.
 7. The system of claim 1, wherein the plurality of droplets ofthe second immiscible liquid are formed to force the solid particles towithin about ten nanometers of the one or more contaminants present onthe surface of the substrate.
 8. The system of claim 1, wherein thecleaning head is structured to form a meniscus of the cleaning solutionbetween the cleaning portion of the cleaning head and the surface of thesubstrate.
 9. The system of claim 1, wherein the first immiscible liquidis a polar solvent and the second immiscible liquid is a non-polarsolvent.
 10. The system of claim 1, wherein the first immiscible liquidis a non-polar solvent and the second immiscible liquid is a polarsolvent.
 11. The system of claim 1, wherein the solid particles areagglomerates of a surface active material.
 12. The system of claim 1,wherein the solid particles are modified to be surface active.
 13. Thesystem of claim 12, wherein the solid particles are surface active byway of ionization.
 14. The system of claim 13, where the pH of the firstimmiscible liquid is set to cause ionization of the solid particles. 15.The system of claim 1, wherein the cleaning solution further includes athird immiscible liquid forming a second plurality of droplets dispersedwithin the first immiscible liquid.
 16. The system of claim 1, whereinthe solid particles are formulated to deform under the force appliedfrom the plurality of droplets of the second immiscible liquid so as tobe imprinted by the one or more contaminants present on the surface ofthe substrate.
 17. The system of claim 16, wherein the solid particlesare deformable to an extent at which a mechanical linkage is establishedbetween the solid particles and the one or more contaminants present onthe surface of the substrate.
 18. The system of claim 1, wherein thesolid particles are softer than the one or more contaminants present onthe surface of the substrate.
 19. The system of claim 1, wherein thesolid particles are substantially uniformly dispersed within the firstimmiscible liquid.
 20. The system of claim 1, further comprising: arinsing portion structured to apply a rinsing fluid to the surface ofthe substrate following application of the cleaning solution to thesurface of the substrate by the cleaning portion; and a drying portionstructured to apply a drying fluid to the surface of the substratefollowing application of the rinsing fluid to the surface of thesubstrate by the rinsing portion.